1. Field of the Invention
This invention relates to restraint devices and more particularly provides a flexible lateral restraint device for an underwater nuclear fuel storage rack.
2. Description of the Prior Art
Nuclear power generating plants are typically fueled by elongated fuel assemblies, such as those including a bundle of nuclear fuel rods. Subsequent to utilization of the fuel assemblies in a nuclear core they are stored within fuel racks positioned within an enclosure such as a spent fuel pit.
A typical spent fuel pit or pool includes leak tight vertical walls and a floor made of concrete and other support materials lined with stainless steel. The fuel racks include a rectangular, closely spaced array of cells, each cell sized to receive a fuel assembly. Because the assemblies have been irradiated they must be shielded, and water is typically utilized for this purpose. The assemblies and fuel racks are therefore maintained submerged within water within the pit.
It is of significant importance that the fuel racks be restrained laterally within the fuel pit under accident conditions, such as a large seismic occurrence. Excessive deflections of the racks and contained fuel assemblies could result in damage to the assemblies and the surrounding environs. It is also recognized that differential thermal expansions can occur in time between the fuel racks and the walls of the containing fuel pit.
Accordingly, several types of lateral restraint devices have been proposed in the past, which respond to these differential expansions as well as seismic occurrences. One type has been proposed which is affixed to the side of the fuel rack and positions, through an arc-like motion between the fuel rack and the containing wall, a load pad surface against the fuel pit wall. A pre-load is imposed upon the pads by a series of Belleville-type springs between a portion of the restraining device and the load pads. With such arc-type devices the pre-load is very difficult to adjust and the device is difficult to properly and accurately position. An excessive amount of space between the fuel rack and the pit wall is also required to accommodate the arc-like motion. Further, the arc motion devices are difficult to properly seat against the pit wall due to the high frictional forces and slippage among the contact pad surface and the pit wall.
A significant improvement upon the arc motion device utilizes the substantially horizontal motion of a device affixed to the side of the rack and remotely extendible into contact with the pit wall. It operates in a manner similar to a scissors jack. This device is described in detail in application Ser. No. 789,912, filed Apr. 22, 1977, in the name of June S. Knight, Personal representative of the estate of Charles B. Knight, deceased, and entitled "Nuclear Fuel Rack Lateral Support and Pre-Load Device".
Among the prior art, the arc-motion devices imposed loads between the racks and walls resulting from differential expansions, as well as imposing loads for pre-load purposes. Thus, the pit walls, for example, are loaded needlessly high. The pre-loaded scissors jack device suffers the same deficiency.
Although these prior art devices will perform the intended function, it is desirable to have an alternative and simple lateral support which avoids unnecessarily high loadings, particularly in new plant installations where remote positioning capability is not necessarily required.